Conventionally, research and development regarding a magnesium base composite material in which magnesium silicide (Mg2Si) particles are dispersed has been energetically carried out. For example, Japanese Unexamined Patent Publication No. 6-81068 discloses a method of manufacturing a magnesium base composite material in which Mg2Si is synthesized by a reaction of Mg of a matrix and Si when a magnesium alloy of high Si content is injection-molded in a semi-solid state, and the Mg2Si particles are dispersed.
In addition, Japanese Unexamined Patent Publication No. 8-41564 discloses a magnesium base composite material provided by a casting method, in which Mg2Si particles and SiC particles are dispersed. In addition, Japanese Unexamined Patent Publication No. 2000-17352 discloses a magnesium base composite material in which spherical Mg2Si particles are dispersed and its manufacturing method by a casting method.
However, all of the above manufacturing methods of the magnesium base composite material are based on a dissolution method such as casting method or an impregnating method. That is, according to the above methods, after magnesium or a magnesium alloy constituting the matrix is dissolved once, it is coagulated and solidified. Therefore, it is observed that the crystal grain diameter of magnesium of the matrix and the Mg2Si particles are coarsely grown, and mechanical characteristics such as strength, hardness and the like are lowered.
Furthermore, according to the above manufacturing methods based on the dissolution method, consumption energy of itself, and especially consumption energy when recycling is considered are surely increased, so that there is a problem regarding costs.
Meanwhile, the inventors of the present invention have proposed a method in which mixture powder provided by combining matrix powder comprising magnesium (Mg) with silicon (Si) powder is pressed to be molded by powder metallurgy technique and this is heated and held at an appropriate solid-phase temperature which is less than a melting point of Mg in a controlled heating atmosphere to generate fine Mg2Si by reaction between Mg and Si powder, so that the fine Mg2Si are dispersed in a matrix. More specifically, “magnesium base composite material, magnesium base composite material precursor, and their manufacturing method” was applied for patent as Patent Application No. 2001-292117, on Sep. 25, 2001 and “magnesium base composite material, magnesium base composite material precursor, and their manufacturing method” was applied for patent as Patent Application No. 2001-292118, on Sep. 25, 2001. These applications are not laid open at this point.
According to the magnesium base composite material provided by the above method proposed by the inventors of the present invention, since fine Mg2Si particles are uniformly dispersed, mechanical characteristics such as strength or hardness of the composite material is improved, and since hard Mg2Si particles are uniformly dispersed, abrasion resistance of the composite material can be improved.
However, when this composite material is used as a material for frictional sliding component, although the abrasion resistance of the composite material itself is improved, there is a problem in which it makes an attack on an opponent material when the opponent material is a relatively soft material.